A xylanase is an enzyme which hydrolyzes xylan or xylan polysaccharides mainly composed of .beta.-1,4-bonded-xyloses to yield its constituents, xylose and xylo-oligosaccharide. The xylanase is present widely in animals and plants. Some microorganisms can also produce xylanases. So far investigations regarding xylanase-producing microorganisms have been made on bacteria, actinomycetes, yeasts, molds and the like.
In these years, keen attention has been brought to the use of xylanases in biomass treatment. More specifically, xylanases are used in enzymatic breakdown of agricultural wastes for production of alcoholic fuels, an enzymatic treatment of animal feeds to release free sugars, an enzymatic treatment for dissolving pulp in the preparation of cellulose and an enzymatic treatment in biobleaching of pulp. In particular, xylanase has been highly expected in the paper and pulp industry wherein xylaneses are used to enhance the brightness of bleached pulp, improve the quality of pulp, decrease the amount of chlorine used in the chemical pulp bleaching steps, and to increase the freeness of pulp in the recycled paper process.
Turning to xylose, this compound is a product of xylan hydrolysis by a xylanase and widely used as a raw material of foods and drugs. Xylo-oligosaccharide which is also a product of xylan hydrolysis is expected to be for use as a sweetener or a moisturizer.
For the use in the foregoing purposes, it is desired to prepare a xylanase suitable for mass production from inexpensive raw materials and having stability to an acid, an alkali and/or heat. Up to date, however, such a xylanase has not been achieved to meet the above requirements.